Process for hydrocarbon conversion



Patented July 27, 1943 PROCESS FOR HYDROCARBON CONVERSIOI" Charles L. Thomas, Chicago, 11]., assignor to Universal Oil Products Company, Chicago, 111., a

corporation of Delaware No Drawing. Application June 13, 1940,

Serial No. 340,243

6 Claims.

This invention is a continuation-in-part of my co-pending application Serial 286,175, filed July 24, 1939. It concerns improvements in catalytic masses suitable for hydrocarbon conversion. More particularly, the invention is related to eatalysts of improved activity comprising essentially chromia-on-alumina. Such catalysts are useful for example in promoting the dehydrogenation of aliphatic hydrocarbons, either of the saturated paraflinic type to the corresponding monoolefin, or of hydrocarbons of the mono-olefinic type having four or five carbon atoms per molecule to the corresponding diolefin. The improved catalysts are also useful in the catalytic reforming of gasolines and naphthas to improve their antiknock character. Straight-chain aliphatic hydrocarbons of six or more carbon atoms per molecule may also be converted to aromatic hydrocarbons by reactions involving both dehydrogenation and cyclization by means of the present catalyst.

The hydrocarbons and hydrocarbon mixtures which are capable of being converted under proper operating conditions by the present improved catalyst include normally gaseous hydrocarbons, such as propane, butane, etc., as well as lowboiling hydrocarbons of the motor fuel boiling range, such as may occur, for example, in straightrun, natural and cracked gasolines obtained by the primary distillation or cracking of petroleum oils and similar hydrocarbonaceous charging stocks.

In one specific embodiment the present invention comprises catalytic material useful for the conversion of aliphatic hydrocarbons which comprises activated alumina containing chromia, the catalytic activity of the composite being promoted by the addition thereto of minor amounts of an oxide of a metal selected from the group consisting of cerium, thorium, and manganese.

The catalysts of the present invention are normally prepared by impregnation, mixing, coprecipitation, and otherwise combining the various constituents under conditions whereby active catalytic composites are obtained. The alumina constituent may be obtained, for example, from various natural ores which are treated to convert them to the oxide form, usually by heating with or without added steam.

A further method of preparing the activated alumina is by the precipitation of aluminum hydroxide from a salt of aluminum, such as aluminum nitrate or aluminum chloride, by the ad dition thereto of ammonium hydroxide or other alkaline precipitants. The chromia constituent may be added by mixing granular or powdered activated alumina with an aqueous solution of chromic acid followed by drying.

Another method comprises mixing activated alumina with chromium trioxide and heating at a temperature of approximately 300 0., whereby the chromium trioxide (CrOz) is converted to the sesquioxide (CrzOa) with the evolution of oxygen.

Another method which has been found useful comprises the coprecipitation of aluminum hydroxide and chromium hydroxide from aqueous solutions of salts such as the nitrates by the addition of ammonium hydroxide, and drying the precipitate. A third component may also be precipitated at the same time.

In another alternative, activated alumina is mixed with a solution of a chromium salt and the hydroxide precipitated by the addition of ammonium hydroxide.

The third component may be added in a number of ways. One convenient method consists in dissolving the oxide or carbonate of the third component in a solution of chromic acid. The activated alumina is then impregnated with mixed hydroxides precipitated from the solution by ammonium hydroxide, dried and calcined.

According to another method, a third component may be added in combination with one of the other constituents such. as, for example, in the form of a soluble chromate such as the dichromate, or it may be added as a salt which is then precipitated on the alumina simultaneously with the chromia. The quantity of chromia in the final mixture may vary considerably deending in part upon the method by which the catalyst is prepared. It is normally of the order of 4-30%, and preferably of the order of 10-20% by weight. The quantity of promoting oxide added to the alumina-chromia catalyst likewise may be varied over a considerable range, but is usually within the range of 0.1-20% by weight, normally 0.110%.

The catalysts of the invention may be used as powders but are usually used in the form of particles such as granules, pellets, etc. Granules of activated alumina may be impregnated, dried, calcined and used without forming or pelleting. when activated alumina powder is used as the starting material, it is impregnated, dried and the powder is mixed with a suitable lubricant such as aluminum stearate, stearic acid, stearic acid and flour, metal powders, etc., and formed by compression methods into shapes such as pellets or spheres which are used as packing material in towers or tubes. I'bllowing this step, the catalyst is calcined at a temperature in excess of 500 C.

The catalyst granules, pellets, spheres, or other suitable shapes are used as packing materials for reactor tubes, reaction chambers, or similar apparatus through which hydrocarbon gases or vapors are passed under proper conditions for conversion.

When used in conjunction with catalytic dehydrogenation, of gaseous hydrocarbons, for example, the temperatures at which conversion takes place are normally within the range of 450-700" C. or higher. The pressure employed may be subatmospheric, atmospheric or slightly superatmospheric of the order of 50-100 pounds per square inch. The time of contact ranges from 0.5 to 6 seconds, although for reforming normally liquid hydrocarbons to increase the antiknock properties, the time of contact may be as high as 60 seconds. Approximately similar conditions are used for producing aromatic hydrocarbons from hydrocarbons having six or more carbon atoms in straight chain arrangement.

During the course of the reactions there is a gradual deposition and accumulation of nonvolatile carbonaceous material on the catalytic surfaces, whereby they are eventually rendered less active. The catalysts can then be reactivated by heating them in the presence of an oxygencontaining gas at temperatures in excess of 500 0., whereby the carbonaceous deposits ar removed to a greater or less degree by combustion.

Although the compounds and particularly the oxides of the elements used in the present invention for increasing the catalytic effect of aluminachromia catalysts are all definitely effective, it is not intended to infer that the diilferent compounds of any one element or the corresponding compounds of difierent elements are exactly equivalent in their promoting eflfect.

The following examples are given to illustrate the usefulness of the present type catalysts but should not be construed as limiting it to the exact conditions given therein, either as to the reaction in which they are employedis concerned, to their components or the exact method of their preparation.

One hundred parts of granular activated alumina were impregnated with a solution of chromic acid followed by drying and reimpregnation until a total of 12% chromia was obtained in the catalytic mass. This reagent was divided into a number of portions for use in the following examples. One portion of the material was calcined at a temperature of 500 C. and used to catalytically dehydrogenate a mixtureof butanes at 600 C., and a contact time of 2 seconds. The yield of butenes when operating over a four-hour period without regeneration amounted to 16% of the original charge.

Example 1 A portion of the alumina-chromia composite was impregnated with a solution of thorium nitrate and the mass was calcined at 500 C. to decompose the nitrate. Its activity for the dehydrogenation of a mixture or butanes under the conditions used with the alumina-chromia was greater than that of the unpromoted material as shown by the fact that 19% of butenes were produced.

Example 2 A portion of the alumina-chromia was impregnated with a solution of manganese nitrate followed by calcining at a temperature of 500 C. The yield of butenes obtained was dehydrogenaing a mixture of butanes under the conditions cited amounted to 26%.

Example 3 A portion of the alumina-chromia was impregnated with cerium nitrate and was then dried and calcined at 500 C. The yield of butenes when dehydrogenating with thi catalyst was 21%.

I claim as my invention:

1. A process for the dehydrogenation of hydrocarbons to produce more valuable products therefrom, which comprises subjecting said hydrocarbons under dehydrogenating conditions to contact with a catalyst comprising alumina and chromia promoted by a minor amount of a compound of cerium;

2. The process of claim 1 further characterized in that said compound of cerium comprises cerium oxide.

3. A process for the dehydrogenation of hydrocarbons to produce more valuable products therefrom, which comprises subjecting said hydrocarbons under dehydrogenating conditions to contact with a catalyst prepared by precipitating the hydroxides of aluminum, chromium and cerium, separating the precipitated material, drying, forming into shapes, and calcining at a temperature in excess of 500 C.

4. A process for the dehydrogenation of hydrocarbons to produce more valuable products therefrom, which comprises subjecting said hydrocarbons under dehydrogenating conditions to contact with a catalyst prepared by impregnating activated alumina powder with an oxide of chromium, drying, further impregnating with a solution of a salt of cerium, precipitating the hydroxide of the last-named metal by the addition thereof of ammonium hydroxide, separating the solid, drying, forming into shapes and calcining at a temperature in excess of 500 C.

5. A process for the dehydrogenation of hydrocarbons to produce more valuable products therefrom, which comprises subjecting said hydrocarbons under dehydrogenating conditions to contact with a catalyst comprising alumina supporting chromium sesquioxide in the proportion of 4-30% by weight of said alumina and cerium oxide in the proportion of 1-10% by weight of said alumina.

6. The process of claim 1 further characterized in that said hydrocarbons comprise aliphatic hydrocarbons.

CHARLES L. THOMAS. 

